RE: How drastically do the economics..There is also the technology using electricity. Sounds weird, but may indeed work very well. We would likely need a huge nuclear reactor in the neighborhood, however, eventually. See recent posts by me about a week ago or so if you are interested for links.
My view is SAGD from natty will be very profitable down to about 5:1 ratio, as long as oil is better than 50 bucks. Why 50? At wti=50 capital cost inflation would reverse over about 18 months to the point that 50 buck wti will be profitable.
I doubt we will ever see 50 bucks unless USA does a 1981-1982 style recession, with the rest of world following it in the following 2 to 3 yrs.
jmho
nb